Add checks for POLICY_AUD

[jillesme]

Summary

I followed https://developers.cloudflare.com/cloudflare-one/identity/authorization-cookie/validating-json/#cloudflare-workers-example without setting the AUD environment variable on accident. That ends up omitting the audience verification entirely. It only verifies if the audience value is set to a truthy value. Even an empty string gets skipped (thanks JavaScript)

I skipped to Go example, because instead of reading from an environment variable, the audience is hard-coded in.

There is also https://github.com/cloudflare/cloudflare-docs/blob/production/src/content/changelog/workers/2025-10-03-one-click-access-for-workers.mdx -- which has the same example. I did not update that yet because I don't know how we feel about retroactively updating changelogs. Happy to update that too.

Screenshots (optional)

Documentation checklist

• The change adheres to the documentation style guide.

[jroyal]

lgtm

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